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Chapter 24
General Genetics- Exam 1
| Question | Answer |
|---|---|
| What are the 5 main types of single-gene inheritance? | Autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked |
| What is a pedigree? | A diagram showing family relationships and hereditary-condition status |
| What is concordance? | The percentage of twin pairs in which both exhibit a trait or disorder |
| What are monozygotic (MZ) twins? | Identical twins formed from the same sperm and egg |
| What are dizygotic (DZ) twins? | Fraternal twins formed from separate sperm-and-egg pairs |
| What is the propositus/proposita? | The person from whom the pedigree is traced |
| Why are human genetic crosses difficult to study? | Controlled matings are impossible and human sibships are relatively small |
| What can make pedigree analysis difficult? | Incomplete penetrance and variable expressivity |
| How does an autosomal dominant trait usually appear? | Usually every generation; both sexes affected equally |
| What happens to offspring of an affected autosomal dominant parent? | On average, half of the children will be affected |
| Can two affected parents have an unaffected child in autosomal dominant inheritance? | Yes |
| What are the three explanations for autosomal dominant disorders? | Haploinsufficiency, gain-of-function, and dominant-negative mutations |
| What is haploinsufficienty? | Having 50% of normal protein is insufficient for a normal phenotype |
| What is a gain-of-function mutation? | A mutation changes a protein so it gains a new function |
| What is a dominant-negative mutation? | The altered gene product acts antagonistically to the normal product |
| What is Huntington disease? | An autosomal dominant disorder causing degeneration of certain brain neurons |
| What protein is mutated in Huntington disease? | Huntingtin |
| What happens to huntingtin in Huntington disease? | A polyglutamine tract is added, causing protein aggregation in neurons |
| What are key signs of autosomal recessive inheritance? | May skip generations; both sexes affected; unaffected parents can have affected children |
| Why are defective enzymes often autosomal recessive? | 50% of normal enzyme in heterozygotes is often sufficient for normal phenotype |
| What is albinism? | Absence or partial deficiency of melanin in skin, eyes, and hair |
| What causes cystic fibrosis? | A mutation affecting the CFTR protein and ion transport |
| What does CFTR regulate? | Ion transport across the cell membrane |
| What problems can cystic fibrosis cause? | Serious digestive and respiratory problems |
| What causes Tay-Sachs disease? | A mutation in the gene encoding hexosaminidase A (HexA) |
| What does HexA normally break down? | GM2 gangliosides, a category of lipids |
| Why do Tay-Sachs symptoms develop? | GM2 gangliosides accumulate in CNS cells, causing neurodegeneration |
| What are key signs of X-linked recessive inheritance? | Usually more males; may skip generations; no father-to-son transmission |
| Why are males especially affected by X-linked recessive traits? | Males have only one copy of most X-linked genes |
| What does hemizygous mean? | Having only one copy of most X-linked genes, as males do |
| What is hemophilia? | A disorder in which blood cannot clot properly |
| What are key signs of X-linked dominant inheritance? | Does not skip generations; affected males pass the trait to daughters, not sons |
| What happens to an affected male's daughters with X-linked dominant inheritance? | All daughters inherit his affected X chromosome |
| What happens to an affected male's sons with X-linked dominant inheritance? | None inherit his affected X because sons receive his Y chromosome |
| What is vitamin D-resistant rickets? | An X-linked dominant disorder caused by lack of phosphate |
| What are defining clues for Y-linked inheritance? | Only males are affected; affected fathers pass it to their sons |
| What is hypertrichosis of the ear? | An example of a Y-linked trait in the slides |
| What is locus heterogeneity? | One disease can result from mutations in two or more different genes |
| What is Hemophilia A genetically? | A defect in clotting factor VIII; it is X-linked recessive |
| What is Hemophilia B genetically? | A defect in clotting factor IX; it is X-linked recessive |
| What causes Hemophilia C and where is its gene? | A defect in clotting factor XI; its gene is on chromosome 4 |
| What is penetrance? | The proportion of people with a genotype who show its phenotype |
| What is the penetrance formula? | % penetrance = affected phenotype ÷ individuals with the relevant genotype |
| What is complete penetrance? | The genotype produces the phenotype in all individuals carrying it |
| What is incomplete penetrance? | Some individuals with the genotype do not show its phenotype |
| How can incomplete penetrance affect a pedigree? | A phenotype may appear to skip a generation |
| What is expressivity? | The degree to which a penetrant gene is phenotypically expressed |
| What is variable expressivity? | The same genotype produces a range of phenotypes |
| What factors can cause incomplete penetrance or variable expressivity? | Gene interactions and environmental effects |
| What is phenylketonuria (PKU)? | An autosomal recessive disorder caused by a defect in phenylalanine hydroxylase |
| What happens in PKU? | Phenylalanine accumulates and is converted to toxic phenylpyruvic acid |
| How is PKU treated according to the slides? | Newborn screening followed by a very low-phenylalanine diet |
| What is a phenocopy? | A phenotype modified to resemble a different mutant organism's phenotype |
| What is phocomelia? | Suppression of limb development; the slides associate it with thalidomide |
| What is the ESP(N) pedigree approach? | Test possible patterns: AD, AR, X-linked dominant, X-linked recessive, and Y-linked |
Created by:
KristenR2025